Sedimentary indicators of water movement in the western approaches to the English Channel

The continental shelf to the southwest of the British Isles is an area of intense tidal current activity. Although most of the sediment is coarse, it still contains a small proportion of fine (<63 μm) material, consisting mainly of biogenic debris. Coccoliths in particular are both common and widespread and they are found in the adjacent slope sediments. The results presented here show that coccolithophorid diversity is high in the deeper parts of Whittard Canyon, the abyssal plain, and on a small area of shelf. Diversity decreases away from the ocean towards the land. Coccoliths and coccospheres have also been recorded from surface water samples. Apart from the landward movement of oceanic water shown by the coccolithophorids, movement of material on the bottom from shelf to slope is shown by the distribution of benthic diatom frustules and mollusc shell chips cut by clionid sponges. Thus, a study of the fine sediment reveals details of sediment transport and water movement.